Effect of <scp> <scp>FeO</scp> </scp> _t Content and <scp> <scp>CaO</scp> </scp> / <scp> <scp>SiO</scp> </scp> ₂ Ratio on Hydrogen Dissolution in <scp> <scp>CaF</scp> </scp> ₂ – <scp> <scp>CaO</scp> </scp> – <scp> <scp>SiO</scp> </scp> ₂ ‐Based Welding Fluxes

Abstract

The solubility of hydrogen in the CaF 2 – CaO – SiO 2 – FeO t slag system was studied to characterize the dependence of hydrogen dissolution behavior on the CaO / SiO 2 ratio and the Fe 3+ / Fe 2+ redox equilibrium at 1823 K. In an acidic slag composition, the dissolved hydrogen seems to exist as an incorporated hydroxyl, where the supplied water vapor reacts with the bridged oxygen ( O o ) of the slag network. In a basic slag composition, hydrogen dissolves as a free hydroxyl in the molten slag by reacting with the free oxygen ( O 2− ). Using FTIR (Fourier transform infrared) and Raman spectroscopy, the addition of FeO t depolymerized the slag structure in an acidic slag system, but polymerized the slag structure in a basic slag system as the FeO t content increased. Furthermore, the formation of γ‐ and δ‐ FeO ( OH ) was controlled by the amount of Fe 2 O 3 present in the flux and increased at higher concentrations of Fe 2 O 3 . At a fixed Fe 2 O 3 content and with CaO / SiO 2 ratios varying from 0.7 to 1.3, the hydrogen solubility curve was parabolic as a function of CaO / SiO 2 , with a minimum near the CaO / SiO 2 ratio of 1.0 and rapidly increasing at CaO / SiO 2 ratios above 1.0.